JP2008270604A - Compound semiconductor solar cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compound semiconductor solar cell having a structure free of cracking and wrinkling of a photoelectric conversion layer caused in a solar cell manufacturing process. <P>SOLUTION: The solar cell includes photoelectric conversion layers (101 and 102) formed principally of a group III-V compound semiconductor, a contact layer (103) formed on the photoelectric conversion layers (101 and 102), and electrodes (105) formed at least partially on a top surface of the contact layer (103), where the contact layer (103) is made principally of GaP and the photoelectric conversion layers are ≤2.5 μm thick. The total of the thickness of the photoelectric conversion layers (101 and 102) and the thickness of the contact layer (103) is preferably ≥3 μm. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a compound semiconductor solar cell, and more particularly to a group III-V compound semiconductor solar cell.

  In recent years, solar cells made of III-V compound semiconductors (hereinafter referred to as III-V group compound semiconductor solar cells) have come to be used for space use or light collection, taking advantage of their high efficiency. ing.

  In the group III-V compound semiconductor solar cell, another solar cell having a small band gap that transmits light having a longer wavelength than the light corresponding to the band gap of the photoelectric conversion layer and absorbs the long wavelength light transmitted through the solar cell. In order to be able to configure a stack type solar cell in combination with the above, it is required to reduce the thickness of the photoelectric conversion layer to the order of μm.

  FIG. 9 is a schematic cross-sectional view showing an example of a conventional III-V group compound semiconductor solar cell in which the photoelectric conversion layer is thinned. The solar cell shown in FIG. 9 includes a photoelectric conversion layer composed of a base layer 901 made of p-InGaP and an emitter layer 902 made of n-InGaP, a contact layer 903 made of n-GaAs formed on the surface side, and A tunnel junction layer 904 made of p + -GaAs / n + -GaAs is formed on the back side. The contact layer 903 and the tunnel junction layer 904 are etched away leaving a pad portion, a comb-shaped portion, and a bar-shaped region connecting them, on which, for example, AuGe / Ni / Au / Ag / Au Thus, electrodes 905 and 906 are respectively formed. Further, interconnectors 907 and 908 are welded to the pad portions of the electrode 905 and the electrode 906, respectively, and a cover glass 909 is bonded to the surface side with a silicon-based resin or the like.

  The solar cell having the structure shown in FIG. 9 is usually manufactured by the method shown in FIG. First, an etching stop layer 1002 made of n-InGaP, a tunnel junction layer 904 made of p + -GaAs / n + -GaAs, a base layer 901 made of p-InGaP, and n-InGaP are formed on a substrate 1001 made of GaAs. An emitter layer 902 and a contact layer 903 made of n-GaAs are formed in this order (FIG. 10A). Next, after applying a resist 1003 on the contact layer 903 (FIG. 10B), a part of the resist 1003 is left by photolithography to form a comb-shaped electrode (FIG. 10C). . Next, the contact layer 903 under the resist 1003 is etched with an ammonia-based etchant (FIG. 10D). At this time, since the underlying emitter layer 902 is not etched in an ammonia system, the etching automatically stops when the contact layer 903 is etched.

  Next, the resist is removed using an appropriate organic solvent (FIG. 10E), and a resist 1004 is applied again on the entire surface (FIG. 10F). By photolithography again, the resist is removed in accordance with the comb-shaped region where the contact layer 903 remains (FIG. 10G). Next, a metal that becomes the surface electrode 905, for example, Au, Ge, Ni, Au, Ag, and Au is deposited in this order (FIG. 10H), and the surface electrode 905 deposited on the resist 1004 by lift-off. Is removed together with the resist 1004, leaving the target electrode on the contact layer 903 (FIG. 10I). The contact layer 903 and the surface electrode 905 are formed by the above process. Note that the surface electrode 905 may be subjected to a heat treatment as necessary to be alloyed to add a process of reducing resistance.

  Next, after the interconnector 907 is welded to the pad portion of the surface electrode 905, the surface side is attached to the cover glass 909 with a silicon-based resin (FIG. 10 (j)). Thereafter, the entire surface of the substrate 1001 is etched using an ammonia-based etchant (FIG. 10 (k)). At this time, etching stops at the etching stop layer 1002. Thereafter, the etching stop layer 1002 is removed with an HCl-based etchant to expose the n + -GaAs layer of the tunnel junction layer 904 made of n + -GaAs (FIG. 10 (l)). Thereafter, the tunnel junction layer is formed in a comb shape by the same process as that for forming the surface electrode 905, and the comb-shaped electrode 906 is formed on the back surface side, for example, AuGe / Ni / Au / Ag / Au. The back side interconnector 908 is welded to the pad portion to obtain the solar cell shown in FIG. 9 (FIG. 10 (m)).

  As described above, the conventional contact layer is usually formed using GaAs (for example, Patent Document 1). However, when GaAs is used for the contact layer and the tunnel junction layer, GaAs has a photoelectric conversion layer. Since the band gap is smaller than that of InGaP, and light in the wavelength band that should be absorbed by InGaP is absorbed by GaAs and does not contribute to power generation, it is necessary to etch the contact layer and the tunnel junction layer in a comb shape. It was.

However, when the contact layer and the tunnel junction layer are etched in a comb shape, only the photoelectric conversion layer is formed so as to spread over the entire surface, and the thickness of the photoelectric conversion layer is on the order of μm. Due to the thinness, there has been a problem that the photoelectric conversion layer is cracked or wrinkled after the process of removing the substrate by etching, especially in the process of making the tunnel junction layer into a comb shape by etching.
JP-A-8-204215

  This invention is made | formed in view of said point, and it aims at providing the solar cell of a structure which does not produce problems, such as a crack of the photoelectric converting layer which generate | occur | produces at the time of a process.

  The solar cell of the present invention includes a photoelectric conversion layer mainly composed of a group III-V compound semiconductor, a contact layer formed on the photoelectric conversion layer, an electrode formed on at least a part of the surface of the contact layer, The contact layer is mainly made of GaP, and the thickness of the photoelectric conversion layer is 2.5 μm or less.

  The total of the thickness of the photoelectric conversion layer and the thickness of the contact layer is preferably 3 μm or more. Moreover, it is preferable that the thickness of the said photoelectric exchange layer is 1-2 micrometers.

The contact layer may be made of Al _x Ga _{1 -xy} In _y P (0 <x ≦ 0.1, 0 <y ≦ 0.1).

  The present invention further includes an intermediate layer between the photoelectric conversion layer and the contact layer, and the band gap and lattice constant of the intermediate layer are the same as the band gap and lattice constant of the photoelectric conversion layer and the band of the contact layer. A solar cell is provided that is between the gap and the lattice constant.

  Furthermore, the present invention is a stack type solar cell having a solar cell (B) connected in series to any one of the solar cells (solar cell (A)), wherein the solar cell (B) has a photoelectric conversion layer. The band gap provides a stacked solar cell that is smaller than the band gap of the photoelectric conversion layer of the solar cell (A).

  The solar cell of the present invention is provided with a contact layer mainly made of GaP on the photoelectric conversion layer. According to such a configuration, it is not necessary to etch the contact layer into a comb shape, and thus the contact layer can be formed over the entire surface, so that cracking and wrinkling of the photoelectric conversion layer during the solar cell manufacturing process is suppressed. be able to.

Hereinafter, the present invention will be described in detail with reference to embodiments.
<First Embodiment>
FIG. 1 is a schematic cross-sectional view showing an example of a solar cell according to the first embodiment of the present invention. The solar cell shown in FIG. 1 includes a photoelectric conversion layer composed of a base layer 101 made of p-InGaP and an emitter layer 102 made of n-InGaP, a contact layer 103 made of n-GaP formed on the surface side, and A tunnel junction layer 104 made of p + -GaAs / n + -GaAs is formed on the back side. The tunnel junction layer 104 is etched away leaving a pad portion, a comb-like portion and a bar-like region connecting them, and electrodes 105 and 106 are formed on the contact layer 103 and the tunnel junction layer 104, respectively. Has been. Further, interconnectors 107 and 108 are welded to the pad portions of the electrode 105 and the electrode 106, respectively, and a cover glass 109 is bonded to the surface side with a silicon-based resin or the like.

  In the present embodiment, unlike the solar cell shown in FIG. 9 described above, the contact layer 103 is made of n-GaP. The contact layer 103 made of n-GaP is an indirect transition type, and has a larger band gap than the photoelectric conversion layer formed of the base layer 101 made of p-InGaP and the emitter layer 102 made of n-InGaP. The light in the wavelength band absorbed by the photoelectric conversion layer and the light in the longer wavelength band are transmitted without loss. Therefore, unlike the case of the contact layer made of n-GaAs shown in FIG. 9, it is not necessary to remove the contact layer by etching in a comb shape leaving a region through which light passes. That is, by using a material mainly composed of GaP having a large band gap as the contact layer, even if the contact layer exists in a portion where light on the surface side is transmitted, the transmission loss can be reduced. It is not necessary to etch in a comb shape. Therefore, the contact layer can be formed on the entire surface of the photoelectric conversion layer, and thereby the thickness can be increased over the entire surface, so that the generation of cracks and wrinkles during the solar cell manufacturing process can be suppressed.

  In the solar cell of this embodiment, the thickness of a photoelectric conversion layer mainly composed of a III-V group compound semiconductor is sufficiently reduced, and light corresponding to the band gap of the photoelectric conversion layer is absorbed to generate power. , Having a function of transmitting light having a longer wavelength than the light corresponding to the band gap. In general, the thickness of the photoelectric conversion layer is required to be about 2.5 μm or less in order to develop the function, but another solar cell is connected in series (tandem) to form a stack type solar cell. In consideration of the conversion efficiency of the stacked solar cell (hereinafter also referred to as a tandem solar cell), a photoelectric conversion layer composed of a base layer 101 made of p-InGaP and an emitter layer 102 made of n-InGaP The thickness is preferably 1 to 2 μm. This point will be described later.

  In the present embodiment, the total of the thickness of the photoelectric conversion layer and the thickness of the contact layer 103 (hereinafter also referred to as total layer thickness) is preferably 3 μm or more. That is, when the thickness of the photoelectric conversion layer is 1 to 2 μm, the thickness of the contact layer is preferably 2 to 1 μm or more, and the total layer thickness is preferably 3 μm or more. When the total layer thickness is less than 3 μm, the rate of occurrence of cracks and wrinkles in the photoelectric conversion layer increases rapidly as the total layer thickness decreases.

  FIG. 2 is a graph showing the relationship between the total layer thickness of the photoelectric conversion layer and the contact layer, cracks, and wrinkle generation rate in the solar cell according to the present embodiment. As can be seen from FIG. 2, when the total layer thickness is less than 3 μm, the rate of occurrence of cracks and wrinkles in the photoelectric conversion layer increases rapidly as the total layer thickness decreases. The occurrence rate of cracks and wrinkles was measured by making the thickness of the photoelectric conversion layer constant at 1.55 μm and variously changing the thickness of the contact layer. Specifically, the occurrence rate of cracks and wrinkles was measured as follows. A total of 300 cells of 1 cm × 1 cm square with a structure of FIG. 1 are manufactured on five 4 ″ -size GaAs substrates per substrate, and the tunnel junction layer 104 is etched into a comb shape and then visually or It observed with the microscope and calculated | required and measured the ratio of the cell number which the crack and wrinkle generate | occur | produced.

  Although there is no restriction | limiting in particular about the upper limit of total layer thickness, Taking into consideration that manufacturing material cost increases, so that a contact layer is thickened, it is preferable to set it as about 5 micrometers or less.

  In the present embodiment, the contact layer 103 is mainly made of GaP. Here, “mainly composed of GaP” means that other components such as Al and In may be included in a range sufficiently larger than the band gap of the photoelectric conversion layer. As described above, when the contact layer is mainly composed of GaP, it is possible to transmit the light in the wavelength band to be absorbed by the photoelectric conversion layer and the light in the longer wavelength band without loss.

The contact layer may contain other components as long as it is mainly composed of GaP. Examples of the other components include Al and In. That is, the contact layer can be made of Al _x Ga _{1 -xy} In _y P.

FIG. 3 is a graph showing the relationship between the composition of the contact layer and the specific resistance in the solar cell according to the present embodiment. FIG. 3A shows the composition of the contact layer as Al _x Ga _1-xy In _y P. FIG. 3B is a graph showing the relationship between the Al composition ratio x and the contact layer resistivity, and FIG. 3B shows the In composition when the contact layer composition is Al _x Ga _{1 -xy} In _y P. It is a graph which shows the relationship between ratio y and the specific resistance of a contact layer. 3A is measured under the condition of In composition ratio y = 0.05, and FIG. 3B is measured under the condition of Al composition ratio x = 0.05. The contact layer only needs to have a band gap larger than that of the photoelectric conversion layer made of InGaP in order to transmit light in the wavelength band to be absorbed by the photoelectric conversion layer and light in a longer wavelength band without loss. Although it is considered that the band gap difference is as large as possible with respect to InGaP. Considering this point, it is considered sufficient to have a band gap equal to or greater than that of the AlInP material having the maximum band gap lattice-matched to the GaAs substrate. Therefore, when the contact layer is Al _x Ga _{1 -xy} In _y P, It is considered preferable that x is 0 to 1.0 and y is generally 0 to 0.2. However, as shown in FIGS. 3A and 3B, when both x and y are greater than 0.1, the specific resistance of the contact layer is remarkably increased, and it is determined that the contact layer is not suitable. Therefore, x and y are each preferably 0.1 or less. The specific resistance of the contact layer was specifically measured as follows. That is, on a GaAs substrate, an _{n-Al x Ga 1-xy} In y P layer to prepare a sample for evaluation was 1μm formed, was measured using a sheet resistance meter by 4 pins.

In this embodiment, a conventionally well-known thing can be used for the dopant of each layer. Further, the carrier concentration is not particularly limited, and is appropriately selected in consideration of series resistance, carrier diffusion length, and the like. For example, when the contact layer 103 made of n-GaP is doped with Si, the carrier concentration can be, for example, about 3 × 10 ¹⁸ to 1 × 10 ¹⁹ cm ⁻³ . Further, when the base layer 101 made of p-InGaP is doped with Zn, the carrier concentration can be, for example, about 1 × 10 ^{17 to} 5 × 10 ¹⁷ cm ⁻³ . When the emitter layer 102 made of n-InGaP is doped with Si, the carrier concentration can be, for example, about 1 × 10 ^{18 to} 5 × 10 ¹⁸ cm ⁻³ .

  Although the manufacturing method of the solar cell of this embodiment is not specifically limited, For example, it can manufacture as follows. FIG. 4 is a schematic process diagram showing a preferred example of the method for manufacturing the solar cell shown in FIG. 1, and shows a schematic cross-sectional view of a solar cell intermediate in each process. First, on a substrate 401 made of GaAs, for example, an etching stop layer 402 made of n-InGaP, a tunnel junction layer 104 made of p + -GaAs / n + -GaAs, a base layer 101 made of p-InGaP, and n-InGaP, for example. The emitter layer 102 made of and the contact layer 103 containing n-GaP as a main component are formed in this order (FIG. 4A).

  Thereafter, an electrode 105 composed of a pad portion and a comb-shaped portion is formed on the contact layer 103 in the same manner as in the method of FIG. 10, for example, by AuGe / Ni / Au / Ag / Au. The interconnector 107 is welded to the cover glass 109 with Si resin or the like (FIG. 4B). Next, the substrate 401 is etched using an ammonia-based etchant or the like (FIG. 4C). Etching is stopped at the etching stop layer 402, and thereafter, the etching stop layer 402 is removed with an HCl-based etching solution (FIG. 4D). Finally, in the same manner as in FIG. 10, the tunnel junction layer 104 on the back surface side is etched away in a comb shape, an electrode 106 is formed, and an interconnector 108 is welded to the pad portion. A solar cell is obtained (FIG. 4E).

<Second Embodiment>
FIG. 5 is a schematic cross-sectional view showing an example of a solar cell according to the second embodiment of the present invention. The solar cell shown in FIG. 5 has a base layer 501 made of p-InGaP and a photoelectric conversion layer made of an emitter layer 502 made of n-InGaP, a contact layer 503 made of n-GaP, and p + formed on the back surface side. A solar cell having the same configuration as that of the solar cell according to the first embodiment, comprising a tunnel junction layer 504 made of -GaAs / n + -GaAs, interconnectors 507 and 508, and a cover glass 509 A stacked solar cell in which a Si solar cell (back contact type) 510 (hereinafter also referred to as a solar cell (B)) is installed under the battery (A)) to form a tandem structure. Here, the band gap of the photoelectric conversion layer of the Si solar cell 510 is smaller than the band gap of the photoelectric conversion layer formed of the base layer 501 made of p-InGaP and the emitter layer 502 made of n-InGaP. Light having a longer wavelength than the light corresponding to the band gap of the photoelectric conversion layer of the solar cell (A) that has passed through the battery (A) is absorbed by the photoelectric conversion layer of the solar cell (B), and the conversion efficiency is greatly improved. is doing.

  FIG. 6 is a graph showing the relationship between the conversion efficiency and the thickness of the photoelectric conversion layer made of InGaP included in the solar cell (A) in the solar cell according to the present embodiment, from p-InGaP in the solar cell (A). The total thickness of the photoelectric conversion layer made of the base layer 501 and the emitter layer 502 made of n-InGaP and the contact layer 503 made of n-GaP is set to 3.5 μm, and the thickness of the photoelectric conversion layer is set to 0.5 μm. It is a graph which shows the conversion efficiency of the whole tandem type solar cell when it changes between -2.5 micrometers, and solar cell (A), (B). As FIG. 6 shows, when the thickness of the photoelectric converting layer of a solar cell (A) is thinner than 1 micrometer, it turns out that the conversion efficiency of a solar cell (A) falls. Moreover, when the thickness of the photoelectric conversion layer of the solar cell (A) is thicker than 2 μm, it is affected by absorption by free carriers of the photoelectric conversion layer, and the long wavelength light transmitted through the solar cell (A) is reduced. It turns out that the conversion efficiency of a solar cell (B) falls. Therefore, the thickness of the photoelectric conversion layer of the solar cell (A) is preferably 1 to 2 μm. If it is in this range, the conversion efficiency of the whole tandem solar cell can be increased.

The conversion efficiency was specifically measured as follows. The light source of the solar simulator is set to AM 1.5 conditions, the tandem solar cell is irradiated with 1 SUN (100 mW / cm ² ), and the output is taken out from the individual electrodes of the solar cells (A) and (B) through the interconnector. The conversion efficiency was measured for each of the solar cells (A) and (B). The conversion efficiency of the tandem solar cell is the sum of the conversion efficiencies of the solar cells (A) and (B).

<Third Embodiment>
FIG. 7 is a schematic cross-sectional view showing an example of a solar cell according to the third embodiment of the present invention. The solar cell shown in FIG. 7 has an n− gap between a contact layer 703 made of n-Gap and a photoelectric conversion layer composed of a base layer 701 made of p-InGaP and an emitter layer 702 made of n-InGaP. The solar cell has the same configuration as that of the solar cell according to the first embodiment except that an intermediate layer 711 made of AlGaInP is provided.

  Here, in the present embodiment, the intermediate layer 711 is an intermediate layer between the contact layer 703 made of n-GaP and the photoelectric conversion layer formed of the base layer 701 made of p-InGaP and the emitter layer 702 made of n-InGaP. It is composed of n-AlGaInP having a band gap and a lattice constant, but the intermediate layer material has a band gap and a lattice constant between the band gap and the lattice constant of the contact layer and the band gap and the lattice constant of the photoelectric conversion layer. What is necessary is just to have. Examples of such a material include AlGaInP, GaInP, AlInP, AlGaInPAs, GaInPAs, AlInPAs, and the like.

FIG. 8 is a conceptual diagram showing a band state in a heterojunction of n-GaP contact layer / n-InGaP photoelectric conversion layer and a heterojunction of n-GaP contact layer / n-AlGaInP intermediate layer / n-InGaP photoelectric conversion layer. . FIGS. 8A and 8B show band states before and after the n-GaP contact layer and the n-InGaP photoelectric conversion layer are heterojunction, respectively. In n-GaP and n-InGaP, the positions of the lower end (Ec) of the conduction band and the upper end (Ev) of the valence band with respect to the vacuum level are in a positional relationship called type II. Large notches (ΔEc and ΔEv, respectively) are generated at the heterointerface (FIG. 8B). In this combination, the notch ΔEc at the conduction band interface is about 0.39 eV, and the notch ΔEv at the valence band interface is about 0.03 eV. A notch of a large conductor of about 0.39 eV at the n-GaP / n-InGaP junction interface may become a barrier (resistance) against electrons, so the carrier concentration of the contact layer and the photoelectric conversion layer at the interface is 3 It is necessary to reduce the resistance by setting a high concentration of × 10 ¹⁸ cm ⁻³ or more so that a tunnel current flows between the notches. However, when the carrier concentration is set to a high concentration in this way, the amount of light absorption by free carriers increases, so that the intensity of light incident on the lower photoelectric conversion layer decreases and the output current of the solar battery cell decreases. is there.

In order to solve the above problem, in this embodiment, an intermediate layer is provided between the contact layer and the photoelectric exchange layer. That is, by forming the heterojunction as n-GaP (contact layer 703) / n-AlGaInP (intermediate layer 711) / n-InGaP (photoelectric conversion layer), as shown in FIG. Is divided into two at each interface (0.39 eV notch is divided into 0.20 eV and 0.19 eV notches), and the carrier concentration of the contact layer and photoelectric conversion layer at the interface is 3 × 10 ¹⁸ cm ⁻³ or less. But resistance doesn't go up.

<Fourth Embodiment>
FIG. 11 is a schematic cross-sectional view showing an example of a solar cell according to the fourth embodiment of the present invention. The solar cell shown in FIG. 11 reverses the conductivity type of the GaP contact layer as compared with the structure of the solar cell according to the first embodiment shown in FIG. It has a structure arranged below. More specifically, a photoelectric conversion layer composed of a base layer 1101 composed of p-InGaP and an emitter layer 1102 composed of n-InGaP, and a tunnel junction layer 1104 composed of p + -GaAs / n + -GaAs formed on the surface side. , And a contact layer 1103 made of p-GaP. The tunnel junction layer 1104 is etched away leaving the pad portion and the comb-shaped portion, and the p-GaP contact layer 1103 is formed on the entire surface. Electrodes 1105 and 1106 are formed on the contact layer 1103 and the tunnel junction layer 1104, respectively. Further, interconnectors 1107 and 1108 are welded to the pad portions of the electrode 1105 and the electrode 1106, respectively, and a cover glass 1109 is bonded to the surface side with a silicon-based resin or the like. Even with such a configuration, the same effect as in the first embodiment can be obtained.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these.

<Example 1>
A III-V compound semiconductor solar cell having the structure shown in FIG. 1 was produced by the method shown in FIG. First, an n-InGaP etching stop layer 402 (0.2 μm thickness, Si-doped: 2 × 10 ¹⁷ cm ⁻³ ), p + -GaAs / n + -GaAs tunnel junction is formed on a GaAs substrate 401. Layer 104 (0.05 μm thickness / 0.25 μm thickness, C doping: 2 × 10 ¹⁹ cm ⁻³ / Te doping: 5 × 10 ¹⁹ cm ⁻³ ), base layer 101 made of p-InGaP (1.5 μm, respectively) Thickness, Zn-doped: 2 × 10 ¹⁷ cm ⁻³ ) and n-InGaP emitter layer 102 (0.05 μm thick, Si-doped: 2 × 10 ¹⁸ cm ⁻³ ), and contact mainly composed of n-GaP A layer 103 (2.0 μm thick, Si-doped: 5 × 10 ¹⁸ cm ⁻³ ) was formed in this order (FIG. 4A).

  Thereafter, an electrode 105 composed of a pad portion and a comb-shaped portion is formed on the contact layer 103 by AuGe / Ni / Au / Ag / Au in the same manner as in the method of FIG. The interconnector 107 was welded and attached to the cover glass 109 with Si-based resin (FIG. 4B). Next, the substrate 401 was etched using an ammonia-based etchant (FIG. 4C). Thereafter, the etching stop layer 402 was removed with an HCl-based etching solution (FIG. 4D). Finally, in the same manner as in FIG. 10, the tunnel junction layer 104 on the back surface side is etched away in a comb shape, an electrode 106 is formed, and an interconnector 108 is welded to the pad portion. A solar cell was obtained (FIG. 4 (e)).

  No cracks or wrinkles were generated when the substrate 401 was removed by etching and when the tunnel junction layer 104 was etched. Moreover, when the conversion efficiency was measured with the said measuring method under AM1.5 for the solar cell of a present Example, it was 18.0%.

<Example 2>
A Si solar cell (back contact type) was installed under the solar cell of Example 1, and a tandem solar cell shown in FIG. 5 was produced. When the conversion efficiency of the Si solar cell with respect to AM1.5 light transmitted through the solar cell having the InGaP photoelectric conversion layer of Example 1 was measured, it was 10.5%, and the efficiency of the tandem type was 28.5%. was gotten.

<Example 3>
Using a method similar to that of Example 1, the contact layer 703 made of n-GaP and the photoelectric conversion layer (made of p-InGaP base layer 701 and n-InGaP emitter layer) shown in FIG. A solar cell having an intermediate layer 711 made of n-AlGaInP was produced. The thickness and carrier concentration of each layer were the same as in Example 1 except for the following layers. Contact layer 703: layer thickness 2.0 μm, Si-doped. The carrier concentration is 5 × 10 ¹⁸ cm ⁻³ only for 0.4 μm on the upper side (electrode 705 side), and 1 × 10 ¹⁸ cm ⁻³ for 1.6 μm on the lower side (intermediate layer 711 side) (intermediate layer 711). : Layer thickness 0.1 μm, Si dope: 1 × 10 ¹⁸ cm ⁻³ ).

  When the substrate was removed by etching and when the tunnel junction layer 704 was etched, no cracks or wrinkles were generated. Moreover, when the conversion efficiency was measured with the said measuring method under AM1.5 for the solar cell of a present Example, it was 18.3%.

<Example 4>
A group III-V compound semiconductor solar cell having the structure shown in FIG. 11 was produced in the same manner as in Example 1. The configuration of each layer was as follows. p-InGaP base layer 1101 (1.5 μm thick, Zn doped: 2 × 10 ¹⁷ cm ⁻³ ), n-InGaP emitter layer 1102 (0.05 μm thick, Si doped: 2 × 10 ¹⁸ cm ⁻³ ), p− GaP contact layer 1103 (2.0 μm thickness, Zn doping: 5 × 10 ¹⁸ cm ⁻³ ), tunnel junction layer 1104 made of p + -GaAs / n + -GaAs (0.05 μm thickness / 0.25 μm thickness, respectively) C dope: 2 × 10 ¹⁹ cm ⁻³ / Te dope: 5 × 10 ¹⁹ cm ⁻³ ).

  When the substrate was removed by etching and when the tunnel junction layer 1104 was etched, no cracks or wrinkles were generated. Moreover, when the conversion efficiency was measured with the said measuring method under AM1.5 for the solar cell of a present Example, it was 18.0%.

<Comparative Example 1>
A solar cell having the structure shown in FIG. 9 was produced by the method of FIG. The configuration of each layer was as follows. p-InGaP base layer 901 (1.5 μm thick, Zn doped: 2 × 10 ¹⁷ cm ⁻³ ), n-InGaP emitter layer 902 (0.05 μm thick, Si doped: 2 × 10 ¹⁸ cm ⁻³ ), n− GaAs contact layer 903 (0.4 μm thick, Te-doped: 5 × 10 ¹⁸ cm ⁻³ ), tunnel junction layer 904 made of p + -GaAs / n + -GaAs (0.05 μm thick / 0.25 μm thick, respectively) C dope: 2 × 10 ¹⁹ cm ⁻³ / Te dope: 5 × 10 ¹⁹ cm ⁻³ ). In FIG. 10, GaAs is used for the substrate, and n-InGaP (0.2 μm thickness, Si doping: 2 × 10 ¹⁷ cm ⁻³ ) is used for the etching stop layer 1002. When the conversion efficiency of this solar cell was measured by the above measurement method under AM 1.5, it was 17.0%.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is a schematic sectional drawing which shows an example of the solar cell which concerns on the 1st Embodiment of this invention. It is a graph which shows the relationship between the total layer thickness of a photoelectric converting layer and a contact layer, a crack, and a wrinkle generation rate in the solar cell which concerns on 1st Embodiment. It is a graph which shows the relationship between the composition of a contact layer and specific resistance in the solar cell which concerns on 1st Embodiment. It is a schematic process drawing which shows a preferable example of the manufacturing method of the solar cell shown by FIG. It is a schematic sectional drawing which shows an example of the solar cell which concerns on the 2nd Embodiment of this invention. It is a graph which shows the relationship between the thickness of the photoelectric converting layer which consists of InGaP which a solar cell (A) has, and the conversion efficiency in the solar cell which concerns on 2nd Embodiment. It is a schematic sectional drawing which shows an example of the solar cell which concerns on the 3rd Embodiment of this invention. It is a conceptual diagram which shows the band state in the heterojunction of n-GaP contact layer / n-InGaP photoelectric conversion layer, and the heterojunction of n-GaP contact layer / n-AlGaInP intermediate | middle layer / n-InGaP photoelectric conversion layer. It is a schematic sectional drawing which shows an example of the conventional III-V group compound semiconductor solar cell. It is a schematic process drawing which shows an example of the manufacturing method of the conventional III-V group compound semiconductor solar cell. It is a schematic sectional drawing which shows an example of the solar cell which concerns on the 4th Embodiment of this invention.

Explanation of symbols

  101, 501, 701, 1101 Base layer, 102, 502, 702, 1102 Emitter layer, 103, 503, 703, 1103 Contact layer, 104, 504, 704, 1104 Tunnel junction layer, 105, 106, 505, 506, 705 , 706, 1105, 1106 electrode, 107, 108, 507, 508, 707, 708, 1107, 1108 interconnector, 109, 509, 709, 1109 cover glass, 401 substrate, 402 etching stop layer, 510 Si solar cell (back Contact type), 711 intermediate layer.

Claims (6)

A photoelectric conversion layer mainly composed of a III-V compound semiconductor;
A contact layer formed on the photoelectric conversion layer;
An electrode formed on at least a part of the surface of the contact layer, and a solar cell comprising:
The contact layer is mainly made of GaP,
The photovoltaic cell, wherein the photoelectric conversion layer has a thickness of 2.5 μm or less.   The solar cell according to claim 1, wherein the total thickness of the photoelectric conversion layer and the thickness of the contact layer is 3 μm or more.   The solar cell according to claim 1, wherein the photoelectric exchange layer has a thickness of 1 to 2 μm. The contact _{layer, Al x Ga 1-xy In} y P (0 <x ≦ 0.1,0 <y ≦ 0.1) the sun according to claim 1, characterized in that it consists battery. Further comprising an intermediate layer between the photoelectric conversion layer and the contact layer,
The band gap and the lattice constant of the intermediate layer are between the band gap and the lattice constant of the photoelectric conversion layer and the band gap and the lattice constant of the contact layer, respectively. The solar cell as described in. A stack type solar cell having a solar cell (B) connected in series to the solar cell (A) according to claim 1,
The solar cell (B) has a photoelectric conversion layer having a band gap smaller than that of the photoelectric conversion layer of the solar cell (A).

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